Question

During early stages of development, dolphin embryos begin to develop hind limbs. By the time the dolphin fetuses are fully developed, the hind limbs have disappeared.

Which statement best explains the early development and then disappearance of hind limbs in dolphins?
A
Dolphin fetuses change their development to adapt to an aquatic environment.
B
The genes that control the development of hind limbs are destroyed as the fetus develops.
C
The early ancestors of dolphins had hind limbs.
D
Dolphins are evolving to become terrestrial animals.

Answer 1

C

The transient hind-limb development in dolphin embryos reflects their evolutionary history: ancestral cetaceans were terrestrial mammals with hind limbs, and embryonic development briefly recapitulates those ancestral features before limb growth is suppressed. Options A and D are incorrect (the change is not an adaptation toward aquatic or terrestrial life during fetal development), and B is wrong because genes aren't destroyed — their expression is turned off.